Rheological Theory and Simulation of Surfactant Nematic Liquid Crystals - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 66

1

(a) t *=2

(b) t *=4

0.5

(c) t *=6

(d) t *=8

0

(e) t *=12

(f) t *=16

(g) t *=20

Figure 2.24 Director out - of - plane component n z profi le after cessation of fl ow, for

R = 0 at the following dimensionless times: (a) t * = 2, (b) 4, (c) 6, (d) 8, (e) 12, (f) 16,

and (g) 20. Er = 1000 of the shear fl ow is applied until t * = 100, and thus the result at

t * 0 (no fl ow). The color scale

on the right indicates the correspondence of the magnitude of n z and the shown colors.
The relaxation of stored elastic energy drives the formation of a spatial pattern.
[Adapted from Tsuji and Rey (1998) .]

= 100 for Er = 1000 corresponds to that at t * = 0 for Er =

periodic oscillations in the shear stress after fl ow reversal were associated with
the possibility that these wormlike micelles are nonaligning:

1. From a
theoretical point of view, the LE model of transient shear rheology predicts
periodic damped stress oscillations for shear startup and fl ow reversal that are
in perfect agreement with stress measurements for a low-molar-mass nonalign-
ing thermotropic N c material (Han and Rey, 1994a-c).
Figure 2.25 shows a characteristic fl ow reversal stress calculation. In fl ow
reversal, the upper plate instantaneously reverses its moving direction at t

λ <

= t rv ,

and the corresponding apparent shear rate γ

used here is